Occupant detecting apparatus capable of improving detection accuracy

ABSTRACT

In an occupant detecting apparatus for detecting an occupant seated on a passenger seat of a vehicle with an airbag for the occupant, a load sensor is provided in a bottom part of the seat. A plurality of first electric field sensors are provided in the bottom part of the seat, and a plurality of second electric field sensors are provided in a rear part of the seat. An airbag inflating permission control unit permits inflation of the airbag in accordance with output signals of the load sensor and the first and second electric field sensors.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an occupant detecting apparatusfor detecting an occupant seated on a passenger seat of a vehicle withan airbag.

[0003] 2. Description of the Related Art

[0004] In a vehicle, an airbag is provided in a driver seat in order toalleviate the impact of a collision. Generally, since an adult is seatedon the driver seat, when any occupant seated on the driver seat isdetected, the inflation of the airbag is always permitted.

[0005] On the other hand, an airbag is also provided in a frontpassenger seat. In this case, since a child or an infant as well as anadult may be seated on the front passenger seat, the permission for theinflation of the airbag depends upon an occupant seated on the frontpassenger seat. Note that, when a child or an infant is seated on thefront passenger seat, if the airbag is inflated, the face of the childor infant is damaged by the inflation of the airbag, which invites amore serious result. Therefore, when a child or an infant is seated onthe front passenger seat, the inflation of the airbag is notpermissible.

[0006] In order to determine whether an occupant seated on the frontpassenger seat is an adult or a child (infant), occupant detectingapparatuses have been developed. As a result, only when an occupantseated on the front passenger seat is an adult, is the inflation of theairbag permitted to protect a child (infant) from being seriouslyinjured.

[0007] A first prior art occupant detecting apparatus is constructed bya load sensor provided on a bottom part of a front passenger seat (see:JP-A-9-207638 and JP-A-10-297334). For example, if the output voltage ofthe load sensor is higher than a reference value, it is determined thatan adult is seat on the front passenger seat. Otherwise, it isdetermined that a child or an infant is seated on the front passengerseat. Note that it is possible to compare the output voltage of the loadsensor with two reference values.

[0008] In the above-described first prior art occupant detectingapparatus, however, when a large luggage is seated on the frontpassenger seat, such a large luggage is considered as an adult to permitthe inflation of the airbag. That is, it is impossible to discriminatean adult from a large luggage.

[0009] A second prior art occupant detecting apparatus is constructed byelectric field sensors (see: JP-A-11-78655). This will be laterexplained in detail. That is, the electric field sensors can detect ahuman body, whether it is an adult, a child or an infant.

[0010] In the above-described second prior art occupant detectingapparatus, however, the electric field sensors detect a wet seat with nooccupant as a human body to permit the inflation of the airbag.

[0011] Thus, both of the first and second prior art occupant detectingapparatuses are inferior in the detection accuracy.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide an occupantdetecting apparatus capable of improving the detection accuracy.

[0013] Another object is to provide an occupant detecting apparatus usedin controlling the inflation of a side-airbag.

[0014] According to the present invention, in an occupant detectingapparatus for detecting an occupant seated on a passenger seat of avehicle with an airbag for the occupant, a load sensor is provided in abottom part of the seat. A plurality of first electric field sensors areprovided in the bottom part of the seat, and a plurality of secondelectric field sensors are provided in a rear part of the seat. Anairbag inflating permission control unit permits inflation of the airbagin accordance with output signals of the load sensor and the first andsecond electric field sensors.

[0015] Also, in an occupant detecting apparatus for detecting anoccupant seated on a passenger seat of a vehicle with an airbag for theoccupant, a plurality of first electric field sensors are provided inthe bottom part of the seat, and a second electric field sensor isprovided in a rear part of the seat. An airbag inflating permissioncontrol unit permits inflation of the airbag in accordance with outputsignals of the first and second electric field sensors.

[0016] Further, in an occupant detecting apparatus for detecting anoccupant seated on a passenger seat of a vehicle with a side-airbag forthe occupant, a load sensor is provided in a bottom part of the seat,and an electric field sensor is provided in a rear part of the seat on aside of the side-airbag. An airbag inflating permission control unitpermits inflation of the side-airbag in accordance with output signalsof the load sensor and said electric field sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be more clearly understood from thedescription set forth below, as compared with the prior art, withreference to the accompanying drawings, wherein:

[0018]FIGS. 1A and 1B are circuit diagrams for explaining the operationof a prior art electric field sensor;

[0019]FIG. 2 is a diagram illustrating a first embodiment of theoccupant detecting apparatus according to the present invention;

[0020]FIG. 3 is a block circuit diagram of the control unit of FIG. 4;

[0021]FIG. 4 is a flowchart showing the airbag inflating operation ofthe control units of FIG. 3;

[0022]FIG. 5 is a flowchart for explaining the airbag inflating flagcalculating operation of the control unit if FIG. 3;

[0023]FIG. 6 is a table showing the flag calculating step of FIG. 5 indetail;

[0024]FIGS. 7A, 7B, 7C, 7D, 7E, 7F, 7G and 7H are diagrams showingobjects seated on the seat of FIG. 2;

[0025]FIG. 8 is a diagram illustrating a second embodiment of theoccupant detecting apparatus according to the present invention;

[0026]FIG. 9 is a block circuit diagram of the control unit of FIG. 8;

[0027]FIG. 10 is a flowchart for explaining the airbag inflating flagcalculating operation of the control unit of FIG. 9;

[0028]FIG. 11 is a table showing the flag calculating step of FIG. 10 indetail;

[0029]FIGS. 12A, 12B, 12C and 12D are diagrams showing objects seated onthe seat of FIG. 8;

[0030]FIG. 13 is a diagram illustrating a third embodiment of theoccupant detecting apparatus according to the present invention;

[0031]FIG. 14 is a block circuit diagram of the control unit of FIG. 13;

[0032]FIG. 15 is a flowchart showing the side-airbag inflating operationof the control units of FIG. 14;

[0033]FIG. 16 is a flowchart for explaining the side-airbag inflatingflag calculating operation of the control unit of FIG. 14;

[0034]FIG. 17 is a table showing the flag calculating step of FIG. 16 indetail;

[0035]FIGS. 18A, 18B and 18C are diagrams showing objects seated on theseat of FIG. 13;

[0036]FIG. 19 is a flowchart for correcting the reference value in theflowcharts of FIGS. 4, 5, 10, 15 and 16;

[0037]FIG. 20 is a diagram showing the arrangement of the antennaelectrodes of FIGS. 2 and 8;

[0038]FIG. 21A is another diagram showing the arrangement of the antennaelectrodes of FIGS. 2 and 8; and

[0039]FIG. 21B is a cross-sectional view taken along the line B-B ofFIG. 21A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] Before the description of the preferred embodiments, a prior artelectric field sensor will be explained with reference to FIGS. 1A and1B.

[0041] As illustrated in FIG. 1A, a high frequency oscillator 101 whosefrequency is about 100 kHz is connected via a resistor 102 to an antennaelectrode 103. Therefore, a differential AC electric field E isgenerated between the antenna electrode 103 and the ground GND, so thata load current I corresponding to the AC electric field E flows throughthe resistor 102. The AC load current I is converted by the resistor 102into an AC voltage which is then transmitted by a voltage buffer 104 toa detector 105 including a bandpass filtering function which generates aDC output voltage V_(out). Note that the antenna electrode 103 ismounted on an automobile seat, for example, and the ground GND indicatesan automobile body.

[0042] As illustrated in FIG. 1B, when an object 0B such as an occupantis seated on the seat, the current flowing between the antenna electrode103 and the ground GND is increased by a shunting current ΔI due to thepresence of the object 0B in the electric field E. As a result, thedetector 105 generates a DC output voltage V_(out)+ΔV larger than the DCoutput voltage V_(out) of FIG. 1A, thus determining whether or not theobject 0B is seated on the automobile seat.

[0043] In FIG. 2, which illustrates a first embodiment of the occupantdetecting apparatus according to the present invention, referencenumeral 1 designates a front passenger seat formed by a bottom part 11and a rear part 12.

[0044] A load sensor 2 formed by a strain gauge or a pressure sensor isprovided between the bottom part 11 of the seat 1 and a vehicle floor(not shown), to measure the weight of an occupant seated on the seat 1.

[0045] Five antenna electrodes 3-1, 3-2, 3-3, 3-4 and 3-5 for electricfield sensors are provided in the bottom part 11 of the seat 1, and fiveantenna electrodes 3-6, 3-7, 3-8, 3-9 and 3-10 for electric fieldsensors are provided in the rear part 12 of the seat 1.

[0046] The load sensor 2 and the antenna electrodes 3-1, 3-2, . . . ,3-10 are connected by a wire harness to a control unit 4 which alsoreceives an output signal from an acceleration sensor 5 to control anairbag inflator 6 for inflating an airbag. For example, the inflator 6includes a source of gun powder, an igniter for igniting the gun powderof the gun powder source, and a generator triggered by the ignition ofthe gun powder for generating pressurized hot gas. That is, when theinflator 6 is driven by the control unit 4, pressurized hot gas isinjected into the airbag 7, thus rapidly inflating the airbag 7.

[0047] In FIG. 3, which is a block circuit diagram of the control unit 4of FIG. 2, the control unit 4 is formed by an analog/digital (A/D)converter 4-1 for performing an A/D conversion upon the output signal ofthe load sensor 2 to generate a digital output load voltage V_(LOAD)depending upon the weight of the occupant seated on the seat 1.

[0048] Also, the control unit 54 is formed by a high frequencyoscillator 4-2, a resistor 4-3, a voltage buffer 4-4 and a detector 4-5corresponding to the high frequency oscillator 101, the resistor 102,the voltage buffer 103 and the detector 104, respectively, of FIGS. 1Aand 1B. One of the antenna electrodes 3-1, 3-2, . . . , 3-10 is selectedby selectors 4-6 and 4-7 and is connected between the resistor 4-3 andthe voltage buffer 4-4. An A/D converter 4-8 performs an A/D conversionupon an output signal of a selected electric field sensor, i.e., aselected antenna electrode to generate a digital output electric fieldvoltage V_(EF).

[0049] Further, an A/D converter 4-9 performs an A/D conversion upon theoutput signal of the acceleration sensor to generate a digital outputacceleration voltage V_(ACC). An input/output interface 4-10 isconnected to the airbag inflator 6.

[0050] The A/D converters 4-1, 4-8 and 4-9 and the input/outputinterface 4-10 are connected to a central processing unit (CPU) 4-11 forcontrolling the entire system, a read-only memory (ROM) 4-12 for storingprograms and fixed data and a random access memory (RAM) for storingtemporary data. The CPU 411 is also connected to the selectors 4-6 and4-7.

[0051] The airbag inflating operation of the control unit 4 (the CPU4-11) of FIG. 3 is explained next with reference to a flowchart of FIG.4 which is carried out at predetermined time intervals.

[0052] First, at step 401, the CPU 4-11 fetches the digital outputacceleration voltage V_(ACC) from the A/D converter 4-9.

[0053] Next, at step 402, it is determined whether the digital outputacceleration voltage V_(ACC) is higher than a reference vale V_(ACCREF),i.e., whether or not a collision has occurred on the front or rear sideof the vehicle. Only when V_(ACC)>V_(ACCREF)) does the control proceedto step 403. Otherwise, the control proceeds directly to step 405.

[0054] At step 403, it is determined whether an airbag inflatingpermission flag FX is “1” or “0”. Note that the setting and resetting ofthe inflation permission flag FX will be explained later. Only when FXis “1”, does the control proceed to step 404 which drives the airbaginflator 6, thus inflating the airbag 7. Otherwise, the control proceedsdirectly to step 405.

[0055] The routine of FIG. 4 is completed by step 405.

[0056] An operation of calculating the airbag inflating permission flagFX of FIG. 4 is explained next with reference to a routine of FIG. 5which is carried out at predetermined time intervals.

[0057] First, at step 501, the CPU 4-11 fetches the digital load voltageV_(LOAD) from the A/D converter 4-1.

[0058] Next, at step 502, the CPU 4-11 fetches the digital outputelectric field voltage V_(EF) (i) from the A/D converter 5-8 where i is1 to 5. In this case, the digital output electric field voltage V_(EF)(i) is obtained when the CPU 4-11 operates the selectors 4-6 and 4-7 sothat the antenna electrode 3-i is connected between the resistor 4-3 andthe voltage buffer 4-4.

[0059] Next, at step 503, an average value V_(EFAV1) is calculated by

V _(EFAV1)←(V _(EF)(1)+V _(EF)(2)+ . . . +V_(EF)(5))/5

[0060] Next, at step 504, the CPU 4-11 fetches the digital outputelectric field voltage V_(EF) (i) from the A/D converter 5-8 where i is6 to 10.

[0061] Next, at step 505, an average value V_(EFAV2) is calculated by

V _(EFAV2)←(V _(EF)(6)+V_(EF)(7)+ . . . +V_(EF)(10))/5

[0062] Next, at step 506, the airbag inflating permission flag FX iscalculated in accordance with the values V_(LOAD), V_(EFAV1), andV_(EFAV2), using a table as shown in FIG. 6 which table is stored in theROM 4-12. That is, it is determined whether V_(LOAD) is higher than areference value V_(LOADREF1), and it is determined whether or notV_(LOAD) is higher than V_(LOAD) ₂ (<V_(LOAD1)). As a result, there arethree states of the voltage V_(LOAD):

[0063] a high state (V_(LOAD)>V_(LOADREF1));

[0064] a medium state (V_(LOAD2)<V_(LOAD)≦V_(LOADREF1)); and

[0065] a low state (0≦V_(LOAD)≦V_(LOAD2))

[0066] Also, it is determined whether or not V_(EFAV1) is higher than areference value V_(EFAVREF1), and it is determined whether or notV_(EFAV1) is higher than a reference value V_(EFAVREF2) (<V_(EFAVREF1)).As a result, there are three states of the voltage V_(EFAV1):

[0067] a high state (V_(EFAV1)>V_(EFAVREF1))

[0068] a medium state (V_(EFAVREF2)<V_(EFAV1)≦V_(EFAVREF1)); and

[0069] a low state (0≦V_(EFAY1)≦V_(EFAVREF2)).

[0070] Further, it is determined whether or not V_(EFAV1) is higher thanthe reference value V_(EFAVREF1), and it is determined whether or notV_(EFAV2) is higher than the reference value V_(EFAVREF2). As a result,there are three states of the voltage V_(EFAV2):

[0071] a high state (V_(EFAV2)>V_(EFAVREF1));

[0072] a medium state (V_(EFAVREF2)<V_(EFAV2)≦V_(EFAVREF1)); and

[0073] a low state (0≦V_(EFAV2)≦V_(EFAVREF2))

[0074] Then, “0” or “1” is allocated to the airbag inflating permissionflag FX in accordance with the table of FIG. 6.

[0075] For example, as illustrated in FIG. 7A, when an adult is surelyseated on the seat 1, the voltage V_(LOAD) is high (>V_(LOADREF1)) andthe voltage V_(EFAV1) and V_(EFAV2) are both high (>V_(EFAVREF1)), SOthat the airbag inflating permission flag FX is set (FX=“1”).

[0076] As illustrated in FIG. 7B, when an adult is seated and leaningforward on the seat 1, the voltage V_(LOAD) is high (>V_(LOADREF1)), thevoltage V_(EFAV1) is high (>V_(EFAVREF1)), and the voltage V_(EFAV2) islow (≦V_(EFAVREF2)), so that the airbag inflating permission flag FX isset (FX=“1”).

[0077] As illustrated in FIG. 7C, when a large luggage is seated on theseat 1, the voltage V_(LOAD) is high (>V_(LOADREF1)), and the voltageV_(EFAV1) and V_(EFAV2) are both low (≦V_(EFAVREF2)), so that the airbaginflating permission flag FX is reset (FX=“0”).

[0078] As illustrated in FIG. 7D, when an infant with an infant seat isseated in a forward facing manner on the seat 1, the voltage V_(LOAD) ismedium (V_(LOADREF1)˜V_(LOADREF2)), the voltage V_(EFAV1) is medium(V_(EFAVREF1)˜V_(EFAVREF2)), and the voltage V_(EFAV2) is high(>V_(EFAVREF1)), so that the airbag inflating permission flag FX is set(FX=“1”).

[0079] As illustrated in FIG. 7E, when a child is surely seated on theseat 1, the voltage V_(LOAD) is medium (V_(LOADREF1)˜V_(LOADREF2)) andthe voltage V_(EFAV1) and V_(EFAV2) are both medium(V_(EFAVREF1)˜V_(EFAVREF2)), so that the airbag inflating permissionflag FX is reset (FX=“0”).

[0080] As illustrated in FIG. 7F, when an infant with an infant seat isseated in a backward facing manner on the seat 1, the voltage V_(LOAD)is medium (V_(LOADREF1)˜V_(LOADREF2)), the voltage V_(EFAV1) is medium(V_(EFAVREF1)˜V_(EFAVREF2)), and the voltage V_(EFAV2) is low(≦V_(EFAVREF2)), so that the airbag inflating permission flag FX isreset (FX=“0”).

[0081] As illustrated in FIG. 7G, when a child is standing on the seat1, the voltage V_(LOAD) is medium (V_(LOADREF1)˜V_(LOADREF2)), thevoltage V_(EFAV1) is low (≦V_(EFAVREF2)), and the voltage V_(EFAV2) ishigh (>V_(EFAVREF1)), so that the airbag inflating permission flag FX isreset (FX=“1”).

[0082] As illustrated in FIG. 7H, when no object is seated on the seat1, the voltage V_(LOAD) is low (≦V_(LOADREF2)), so that the airbaginflating permission flag FX is reset (FX=“0”), regardless of whetherthe seat 1 is dry or wet.

[0083] Then, the routine of FIG. 5 is completed by step 507.

[0084] In the above-described first embodiment, a plurality of electricfield sensors other than the five electric field sensors can be providedon the bottom part 11 of the seat 1, and also, a plurality of electricfield sensors other than the five electric field sensors can be providedon the rear part 12 of the seat 1. Also, the reference valuesV_(EFAVREF1) and V_(EFAVREF2) can be different values for the averagevoltages V_(EFAV1) and V_(EFAV2).

[0085] In FIG. 8, which illustrates a second embodiment of the occupantdetecting apparatus according to the present invention, only the antennaelectrode 3-10 is provided in the rear part 12 of the seat 1. In thiscase, the antenna electrode 3-10 is used for determining whether or notan object seated on the seat 1 is higher than a predetermined value.Also, the load sensor 2 of FIG. 2 is not provided.

[0086] In FIG. 9, which is a block circuit diagram of the control unit 4of FIG. 8, one of the antenna electrodes 3-1, 3-2, . . . , 3-5 and 3-10is selected by selectors 4-6 and 4-7 and is connected between theresistor 4-3 and the voltage buffer 4-4.

[0087] The airbag inflating operation of the control unit 4 (the CPU4-11) of FIG. 9 is the same as that as in the flowchart of FIG. 4.

[0088] An operation of calculating the airbag inflating permission flagFX of FIG. 4 is explained next with reference to a routine of FIG. 10which is carried out at pretermined time intervals.

[0089] First, at step 1001, the CPU 4-11 fetches the digital outputelectric field voltage V_(EF) (i) from the A/D converter 5-8 where I is1 to 5. In this case, the digital output electric field voltage V_(EF)(i) is obtained when the CPU 5-11 operates the selectors 5-6 and 5-7 sothat the antenna electrode 3-i is connected between the resistor 4-3 andthe voltage buffer 4-4.

[0090] Next, at step 1002, an average value V_(EFAV) is calculated by

V_(EFAV)←(V _(EF)(1)+V _(EF)(2)+ . . . +V_(EF)(5))/5

[0091] Next, at step 1003, the CPU 4-11 fetches the digital outputelectric field voltage V_(EF) (10) from the A/D converter 5-8.

[0092] Next, at step 1004, the airbag inflating permission flag FX iscalculated in accordance with the values V_(LOAD), V_(EFAV)) andV_(EF)(10), using a table as shown in FIG. 11 which table is stored inthe ROM 4-12. That is, it is determined whether or not V_(EFAV) ishigher than a reference value V_(EFAVREF1), and it is determined whetheror not V_(EFAV) is higher than a reference value V_(EFAVREF2)(<V_(EFAVREF1)). As a result, there are three states of the voltageV_(EFAV):

[0093] a high state (V_(EFAV)>V_(EFAVREF1));

[0094] a medium state (V_(EFAVREF2)<V_(EFAV)≦V_(EFAVREF1)); and

[0095] a low state (0≦V_(EFAV)≦V_(EFAVREF2)).

[0096] Further, it is determined whether or not V_(EF)(10) is higherthan the reference value V_(EFREF). As a result, there are two states ofthe voltage V_(EFAV2)):

[0097] a high state (V_(EF)(10)>V_(EFREF)); and

[0098] a low state (0≦V_(EF)(10)≦V_(EFREF)).

[0099] Then, “0” or “1” is allocated to the airbag inflating permissionflag FX in accordance with the table of FIG. 11.

[0100] For example, as illustrated in FIG. 12A, when an adult is surelyseated on the seat 1, the voltages V_(EFAV) and V_(EF)(10) are bothhigh, so that the airbag inflating permission flag FX is set (FX=“1”).

[0101] As illustrated in FIG. 12B, when a adult with a cushion is seatedon the seat 1, the voltages V_(EFAV) and V_(EF)(10) are medium and high,respectively, so that the airbag inflating permission flag FX is set(FX=“1”).

[0102] As illustrated in FIG. 12C, when a child is surely seated on theseat 1, the voltages V_(EFAV) and V_(EF)(10) are medium and low,respectively, so that the airbag inflating permission flag FX is reset(FX=“0”).

[0103] As illustrated in FIG. 12D, when a child with a cushion is seatedon the seat 1, the voltage V_(EFAV) and V_(EF)(10) are both low, so thatthe airbag inflating permission flag FX is reset (FX=“0”).

[0104] Then, the routine of FIG. 10 is completed by step 1005.

[0105] In the above-described second embodiment, a plurality of electricfield sensors other than the five electric field sensors can be providedon the bottom part 11 of the seat 1.

[0106] In FIG. 13, which illustrates a third embodiment of the occupantdetecting apparatus according to the present invention, referencenumeral 1 designates a front passenger seat formed by a bottom part 11and a rear part 12.

[0107] A load sensor 2 formed by a strain gauge or a pressure sensor isprovided between the bottom part 11 of the seat 1 and a vehicle floor(not shown), to measure the weight of an occupant seated on the seat 1.

[0108] An antenna electrode 3′ for an electric field sensor is providedon the side of the rear part 12 of the seat 1.

[0109] The load sensor 2 and the antenna electrode 3′ are connected bywire harness to a control unit 4 which also receives an output signalfrom a traverse acceleration sensor 5′ to control a side-airbag inflator6′ for inflating a side-airbag 7′. That is, when the inflator 6′ isdriven by the control unit 4, pressurized hot gas is injected into theside-airbag 7′, thus rapidly inflating the side-airbag 7′.

[0110] Note that the side-airbag 7′ is located next to the antennaelectrode 3′.

[0111] In FIG. 14, which is a block circuit diagram of the control unit4 of FIG. 13, the selectors 406 and 407 of FIG. 3 are not provided, andtherefore, the antenna electrodes 3′ is always connected between theresistor 4-3 and the voltage buffer 4-4.

[0112] The side-airbag inflating operation of the control unit 4 (theCPU 4-11) of FIG. 14 is explained next with reference to a flowchart ofFIG. 15 which is carried out at predetermined time intervals.

[0113] First, at step 1501, the CPU 4-11 fetches the digital outputacceleration voltage V_(ACC)′ from the A/D converter 4-9.

[0114] Next, at step 1502, it is determined whether the digital outputacceleration voltage V_(ACC)′ is higher than a reference valeV_(ACCREF), i.e., whether or not a collision has occurred on thetraverse side of the vehicle. Only when V_(ACC)′>V_(ACCREF)′, does thecontrol proceed to step 1503. Otherwise, the control proceeds directlyto step 1505.

[0115] At step 1503, it is determined whether a side-airbag inflatingpermission flag FX′ is “1” or “0”. Note that the setting and resettingof the inflation permission flag FX′ will be explained later. Only whenFX′ is “1”, does the control Proceed to step 1504 which drives theside-airbag inflator 6′, thus inflating the airbag 7′. Otherwise, thecontrol proceeds directly to step 1505.

[0116] The routine of FIG. 15 is completed by step 1505.

[0117] An operation of calculating the side-airbag inflating permissionflag FX′ of FIG. 15 is explained next with reference to a routine ofFIG. 16 which is carried out at predetermined time intervals.

[0118] First, at step 1601, the CPU 4-11 fetches the digital loadvoltage V_(LOAD) from the A/D converter 4-1.

[0119] Next, at step 1602, the CPU 4-11 fetches the digital outputelectric field voltage V_(EF) from the A/D converter 48.

[0120] Next, at step 1603, the side-airbag inflating permission flag FX′is calculated in accordance with the values V_(LOAD) and V_(EF) using atable as shown in FIG. 17 which table is stored in the ROM 4-12. Thatis, it is determined whether V_(LOAD) is higher than a reference valueV_(LOADREF1)) and it is determined whether V_(LOAD) is higher thenV_(LOADREF2) (<V_(LOADREF1)). As a result, there are three states of thevoltage V_(LOAD):

[0121] a high state (V_(LOAD)>V_(LOADREF1));

[0122] a medium state (V_(LOADREF2)<V_(LOAD)−V_(LOADREF1)); and

[0123] a low state (0≦V_(LOAD)≦V_(LOADREF2))

[0124] Also, it is determined whether or not V_(EF) is higher than areference value V_(EFREF1), and it is determined whether or not V_(EF)is higher than a reference value V_(EFREF2) (<V_(EFREF1)). As a result,there are three states of the voltage V_(EF):

[0125] a high state (V_(EF)>V_(EFREF1));

[0126] a medium state (V_(EFREF2)<V_(EF)≦V_(EFREF1)); and

[0127] a low state (0≦V_(EF)≦V_(EFREF2)).

[0128] Then, “0” or “1” is allocated to the side-airbag inflatingpermission flag FX′ in accordance with the table of FIG. 17.

[0129] For example, when an adult is surely seated on the seat 1, thevoltage V_(LOAD) is high (>V_(LOADREF)), so that the side-airbaginflating permission flag FX′ is set (FX=“1”) regardless of the voltageV_(EF).

[0130] As illustrated in FIG. 18A, when a child is seated on the seat 1and leans to the antenna electrode 3′, the voltage V_(LOAD) is medium(V_(LOADREF1)˜V_(LOADREF2)), and the voltages V_(EF) is high(>V_(EFREF1)), so that the side-airbag inflating permission flag FX′ isreset (FX=“0”).

[0131] As illustrated in FIG. 18B, when a child is seated on the seat 1,the voltage V_(LOAD) is medium (V_(LOADREF1)˜V_(LOADREF2)) and thevoltage V_(EF) is medium (V_(EFAVREF1)˜V_(EFAVREF2)), so that theside-airbag inflating permission flag FX′ is set (FX=“1”).

[0132] As illustrated in FIG. 18C, when a child is seated on the seat 1and leans to the opposite side of the antenna electrode 3′, the voltageV_(LOAD) is medium (V_(LOADREF1)˜V_(LOADREF2)) and the voltage V_(EF) islow (≦V_(EFREF2)), so that the side-airbag inflating permission flag FX′is set (FX=“1”).

[0133] Then, the routine of FIG. 16 is completed by step 1604.

[0134] In the above-mentioned embodiments, the reference values suchV_(LOADREF1), V_(LOADREF2), V_(EFAVREF1), V_(EFAVREF1), V_(EFREF1) andV_(EFREF2) can be corrected as occasion demands. For example, when noobject is seated in the seat 1, the driver initiates a flowchart asillustrated in FIG. 19 which corrects the reference value V_(EFREF1) inthe third embodiment. That is, at step 1901, the CPU 4-11 fetches theoutput voltage V_(EF) from the A/D converter 4-8. Next, at step 1902, itis determined whether or not V_(EF) is higher than the reference valueV_(EFREF2). In this case, V_(EF)≦V_(EFREF2) is expected. However, ifV_(EF)>V_(EFREF2), the control proceeds to step 1903 which increasesV_(EFREF2) by α. Then, the control is completed by step 1904. Otherreference values such as V_(LOADREF2) can be corrected by similarmethods.

[0135] As illustrated in FIG. 20, the antenna electrodes 3-1, 3-2, . . ., 3-5 of FIGS. 2 and 8 are provided on the front and back surfaces of abase cloth 201 covered by a seat cover 202 on the bottom part 11 of theseat 1. In this case, the antenna electrodes 3-1, 3-3 and 3-5 areadhered to the back surface of the base cloth 201, while the antennaelectrodes 3-2 and 3-4 are adhered to the front surface of the basecloth 201, thus smoothing the seat cover 202. In this case, the wireharness of the antenna electrodes 3-2 and 3-4 penetrate the base cloth201.

[0136] Also, the antenna electrodes 3-1, 3-2, . . . , 3-5 of FIGS. 2 and8 can be provided as illustrted in FIG. 21A and FIG. 21B which is across-sectional view taken along the line B-B of FIG. 21A. That is, theantenna electrode 3-2 has an extension 3-2 a on the side of the basecloth 201 and an extension 3-2 b on the back surface of the base cloth201. Also, the antenna electrode 3-4 has the same configuration as theantenna electrode 3-2. As a result, the part of the wire harness throughthe base cloth 201 of FIG. 20 is unnecessary, which further smooths theseat cover 202. In addition, the reliability of the electric fieldsensors can be improved as compared with those of FIG. 20.

[0137] In the above-described first and second embodiments, although theaverge value of the output signals of the electric field sensors iscalculated, the permission flag can be calculated in accordance with thepattern of the output signals of the electric field sensors.

[0138] Also, the present invention can be applied to a rear passengerseat.

[0139] As explained hereinabove, according to the present invention,since a plurality of electric field sensors are provided in a passengerseat and the presence or absence of an occupant in the seat isdetermined in accordance with a logic processing of the output signalsof the electric field sensors, the detection accuracy of an occupant inthe seat can be improved.

[0140] Also, the presence or absence of an occupant in the seat isdetermined in accordance with the combination of an output signal of aload sensor provided in the seat with the output signals of the electricfield sensors, the detection accuracy of an occupant can be furtherimproved.

1. An occupant detecting apparatus for detecting an occupant seated on apassenger seat of a vehicle with a side-airbag for said occupant,comprising: a load sensor provided in a bottom part of said seat; anelectric field sensor provided in a rear part of said seat on a side ofsaid side-airbag; and an airbag inflating permission control unit,connected to said load sensor and said electric field sensor, forpermitting inflation of said side-airbag in accordance with outputsignals of said load sensor and said electric field sensor.
 2. Theapparatus as set forth in claim 1, wherein said airbag inflatingpermission control unit compares an output signal of said load sensorwith first and second load reference value, and compares the outputsignal of said electric field sensor with first and second electricfield reference values, said first load reference value being higherthan said second load reference value, said first electric fieldreference value being higher than said second electric field referencevalue.
 3. The apparatus as set forth in claim 2, wherein when the outputsignal of said load signal is between said first and second loadreference values, and the output signal of said electric field sensor ishigher than said first electric field reference value, said airbaginflating permission control unit determines that a child is seated onsaid seat and leans to said electric field sensor not to permit theinflation of said airbag.
 4. The apparatus as set forth in claim 2,wherein when the output signal of said load signal is between said firstand second load reference values, and the output signal of said electricfield sensor is between said first and second electric field referencevalues, said airbag inflating permission control unit determines that achild is surely seated on said seat to permit the inflation of saidairbag.
 5. The apparatus as set forth in claim 2, wherein when theoutput signal of said load signal is between said first and secondoadreference values, and the output signal of said electric field sensor islower than said second electric field reference value, said airbaginflating permission control unit determines that a child is seated onsaid seat and leans to an opposite side of said electric field sensor topermit the inflation of said airbag.
 6. An occupant detecting apparatusfor detecting an occupant seated on a passenger seat of a vehicle withan airbag for said occupant, comprising: a plurality of first electricfield sensors provided in the bottom part of said seat; a secondelectric field sensor provided in a rear part of said seat; and anairbag inflating permission control unit, connected to said first andsecond electric field sensors, for permitting inflation of said airbagin accordance with output signals of said first and second electricfield sensors.
 7. The apparatus as set forth in claim 6, wherein saidairbag inflating permission control unit corrects said second loadreference value and said second electric field reference value when noobject is seated on said seat.